The present invention relates to electrolytes used in electrochemical devices, and more particularly, to colloidal electrolytes having increased conductivity in the electrochemical device compared to the conductivity of the liquid electrolyte alone.
The use of liquid electrolytes in electrochemical devices presents a number of difficulties. First, the electrolytes are often corrosive, and they can be difficult to contain. For example, lead storage batteries use sulfuric acid as the electrolyte. If the sulfuric acid corrodes through the container, it can create environmental problems. As a result, attempts have been made to immobilize liquid electrolytes. These efforts have had varying degrees of success. In addition, many organic electrolytes are flammable.
Furthermore, the performance of electrochemical devices can suffer under low or high temperature conditions. For example, cold temperatures reduce the conductivity of the current solid or liquid electrolytes used in lithium batteries. At temperatures less than −20° C., some liquid electrolytes freeze, resulting in a major drop in ionic conductivity and capacity. In addition, cold temperatures slow down the charge transfer reaction kinetics at the electrode-electrolyte interfaces. Thus, when liquid electrolytes are used in an electrochemical device such as a lithium ion battery, the rate capability and performance of the battery is slowed as a result of the effect of the cold temperature on the liquid electrolytes. Under high temperature conditions, liquid electrolytes can suffer from instability and degradation, which is believed to be due primarily to the decomposition of the lithium salt, such as LiPF6.
Attempts have been made to decrease the effect of cold temperatures on liquid electrolytes and, consequently, to improve the performance of the electrochemical devices containing them. For example, insulating blankets, heaters, and phase change materials have been developed to keep liquid electrolytes warm in lithium ion and other batteries. Although these efforts have helped to improve the conductivity of the electrolytes and the charge transfer reaction kinetics of lithium ion batteries under cold temperature conditions, they increase the cost per kilowatt-hour, and they lower the energy and power densities of the battery.
Thus, there is a need for an electrolyte composition which can maintain good conductivity under a wide range of temperatures.